Why we must avoid temperature overshoot

Date:
November 29, 2021
Source:
International Institute for Applied Systems Analysis
Summary:
A new international study shows how near-term mitigation can help
to prevent an overshoot in global temperatures, thereby reducing
climate risks and bringing long-term economic gains.



FULL STORY ==========================================================================
A new international study coordinated by IIASA shows how near-term
mitigation can help to prevent an overshoot in global temperatures,
thereby reducing climate risks and bringing long-term economic gains.


==========================================================================
The Paris Agreement's goal is to hold global warming to well below 2DEGC,
and pursue efforts to limit it to 1.5DEGC. But what path should the world
take to reach this desirable destination? The study just published in
Nature Climate Change led by IIASA Energy, Climate, and Environment
Program Director, Keywan Riahi provides some answers. The study
summarizes insights from nine leading integrated assessment research
teams exploring how to design cost-effective and feasible pathways to
meet the Paris goals.

Scientists use integrated assessment models to explore options for climate policy. These look at the human activities driving emissions -- forms
of energy generation, efficiency measures, and changes in land use --
and calculate the costs of deploying them over coming decades. Models
adjust these factors to meet a given goal for the lowest cost.

So far, most studies have focused on the distant future, requiring
only that the Paris goals are achieved by the end of the 21st
century. Consequently, almost all of the resulting scenarios allow global temperature to overshoot in mid-century, only later turning the dial
back down again. In order to reverse the overshoot, they make a heavy
demand: requiring the world to achieve net- negative emissions to reduce
the amount of carbon dioxide in the atmosphere and thereby decrease the temperature level.

Negative emissions on such a huge scale may however turn out not to be feasible; and even a temporary overshoot would increase hazards such as flooding and wildfires, and could cause permanent damage to the climate
and fragile ecosystems. It would be much better not to stray into such dangerous territory.

"The study for the first time systematically compares scenarios that
avoid overshoot across models. Rapid emissions cuts in the next few
decades would mean that there is no need to go net-negative: instead,
global temperatures would plateau at a given level around the time
we reach net-zero emissions. We also found that models agree on many implications for regional energy systems like the rapid decarbonization
of the power sector," says Christoph Bertram, a study coauthor from the
Potsdam Institute for Climate Impact Research.

As well as being safer for the planet, this turns out to have long-term economic benefits. The study projects that global GDP in 2100 would be
up to 2% higher in scenarios that avoid overshoot.

"We show that up-front investment to achieve rapid transformations towards
a global net-zero system will pay off in the long term," says Riahi.

"In fact, the benefit is likely to be greater still, as this calculation
does not include the economic impacts of climate change, which would be
more severe in overshoot scenarios," adds coauthor Laurent Drouet from
the Euro- Mediterranean Center on Climate Change (CMCC) in Italy who led another paper in the same issue of Nature Climate Change, illustrating
the benefits in terms of the avoided climate change impacts.

"Scenario results show consistently across models that the transportation sector will be the decarbonization laggard. Consequently, a
'mobility revolution' will be crucial to reducing dependence on net-negative-emissions technologies and to mitigate their risks and
negative societal impacts," notes coauthor Daniel Huppmann, a researcher
in the IIASA Integrated Assessment and Climate Change Research Group.

The study by Riahi and colleagues also highlights the urgent need
to improve climate ambition. It shows that if we follow existing
Nationally Determined Contributions (NDCs -- each country's stated
aim for emissions to 2030), the 1.5DEGC threshold will be exceeded,
in contrast to the stated ambition at the recent climate conference
(COP26) in Glasgow. Following current pledges until 2030 imply a slow
start to mitigation efforts, and the models simply cannot see a way to
ramp up decarbonization fast enough after that to reach the Paris goals,
no matter how hard we try.

The study is part of the Exploring National and Global Actions to reduce Greenhouse gas Emissions (ENGAGE) project funded by the European Union's Horizon 2020 research and innovation program Grant No 821471.

========================================================================== Story Source: Materials provided by International_Institute_for_Applied_Systems_Analysis.

Note: Content may be edited for style and length.


========================================================================== Journal References:
1. Laurent Drouet, Valentina Bosetti, Simone A. Padoan, Lara Aleluia
Reis,
Christoph Bertram, Francesco Dalla Longa, Jacques Despre's, Johannes
Emmerling, Florian Fosse, Kostas Fragkiadakis, Stefan Frank,
Oliver Fricko, Shinichiro Fujimori, Mathijs Harmsen, Volker Krey,
Ken Oshiro, Larissa P. Nogueira, Leonidas Paroussos, Franziska
Piontek, Keywan Riahi, Pedro R. R. Rochedo, Roberto Schaeffer,
Jun'ya Takakura, Kaj-Ivar van der Wijst, Bob van der Zwaan,
Detlef van Vuuren, Zoi Vrontisi, Matthias Weitzel, Behnam Zakeri,
Massimo Tavoni. Net zero-emission pathways reduce the physical
and economic risks of climate change. Nature Climate Change, 2021;
DOI: 10.1038/s41558-021-01218-z
2. Keywan Riahi, Christoph Bertram, Daniel Huppmann, Joeri Rogelj,
Valentina
Bosetti, Anique-Marie Cabardos, Andre Deppermann, Laurent
Drouet, Stefan Frank, Oliver Fricko, Shinichiro Fujimori, Mathijs
Harmsen, Tomoko Hasegawa, Volker Krey, Gunnar Luderer, Leonidas
Paroussos, Roberto Schaeffer, Matthias Weitzel, Bob van der
Zwaan, Zoi Vrontisi, Francesco Dalla Longa, Jacques Despre's,
Florian Fosse, Kostas Fragkiadakis, Mykola Gusti, Florian
Humpeno"der, Kimon Keramidas, Paul Kishimoto, Elmar Kriegler,
Malte Meinshausen, Larissa P. Nogueira, Ken Oshiro, Alexander
Popp, Pedro R. R. Rochedo, Gamze U"nlu", Bas van Ruijven,
Junya Takakura, Massimo Tavoni, Detlef van Vuuren, Behnam
Zakeri. Cost and attainability of meeting stringent climate
targets without overshoot. Nature Climate Change, 2021; DOI:
10.1038/s41558-021-01215-2 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/11/211129122807.htm

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